3-D structures having high temperature stability and improved microporosity

ABSTRACT

The present invention relates to 3-D structures having high temperature stability and improved micro-porosity as well as processes of making and using same. The disclosed 3-D are advantageous because they have low densities and low permittivities. When compared to previous 3-D structures, the present structures maintain their low permittivities over a broader range of electromagnetic frequencies. Thus, when used in communication devices such as array antennas, can provided higher communication performance in high temperature environments.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional ApplicationSer. No. 62/886,011 filed Aug. 13, 2019, the contents of which is herebyincorporated by reference in their entry.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

FIELD OF THE INVENTION

The present invention relates to 3-D structures having high temperaturestability and improved micro-porosity as well as processes of making andusing same.

BACKGROUND OF THE INVENTION

3-D printed structures are used for a number of purposes, including butnot limited to high temperature communication applications.Unfortunately, current 3-D structures, including 3-D printed structures,do not offer the combination of high temperature stability and lowpermittivities over a broader range of electromagnetic frequencies thatis desired for use in high temperature application communicationdevices.

Applicants recognized that the source of the aforementioned problem liein the lack of micro-porosity found in 3-D structures made from hightemperature polymers such as polyimides. Applicants solved such problemby creating a method for making a 3-D structure wherein tuneablemicro-porosities can be obtained as a result of the judicious selectionof the 3-D printing ink and the processing conditions under which suchink is 3-D printed. While not being bound by theory, Applicants believethat when a proper level of intrinsic micro-porosity is processed into a3-D article, the air in the 3-D structure's micro-pores acts as adielectric modifier. Thus, low permittivities over a broader range ofelectromagnetic frequencies can be obtained from the 3-D structure.

SUMMARY OF THE INVENTION

The present invention relates to 3-D structures having high temperaturestability and improved micro-porosity as well as processes of making andusing same. The disclosed 3-D structures are advantageous because theyhave low densities and low permittivities. When compared to previous 3-Dstructures, the present structures maintain their low permittivitiesover a broader range of electromagnetic frequencies. Thus, when used incommunication devices such as array antennas, can provided highercommunication performance in high temperature environments.

Additional objects, advantages, and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description of the embodiments givenbelow, serve to explain the principles of the present invention.

FIG. 1 is a plot displaying sample yield stress determination principlefor inks.

FIG. 2 . is a plot displaying paper loading frame for samples of tensileproperties measurement.

FIG. 3 . is a plot displaying a customized shim for tensile propertiesmeasurement.

FIG. 4 . is a plot displaying sample glass transition temperature (Tg)of printed materials.

FIG. 5A. is a top view of a customized holder for 4-mL and 20-mL vial

FIG. 5B is an isometric view of a customized holder for 4-mL and 20-mLvial

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the sequence of operations as disclosedherein, including, for example, specific dimensions, orientations,locations, and shapes of various illustrated components, will bedetermined in part by the particular intended application and useenvironment. Certain features of the illustrated embodiments have beenenlarged or distorted relative to others to facilitate visualization andclear understanding. In particular, thin features may be thickened, forexample, for clarity or illustration.

DETAILED DESCRIPTION OF THE INVENTION Definitions

As used herein a “three dimensional article” is defined as an articlehaving a geometric structure that cannot be defined by a fixed distanceprojection of a two-dimensional pattern perpendicular to the surfacecontaining the pattern and/or where the 3 major dimensions of thesmallest rectangular prism bounding the article are such that thesmallest dimension is larger than 10% of the next largest dimensionwhich is larger than 10% of the largest dimension.

As used herein, the term miscible means forming at at least onetemperature and pressure range combination, over the range of 15° C. to60° C. and pressure range of 0.0001 atm to 2 atm, a homogenous solutionwithout active demixing or phase separating behavior.

Unless specifically stated otherwise, as used herein, the terms “a”,“an” and “the” mean “at least one”.

As used herein, the terms “include”, “includes” and “including” aremeant to be non-limiting.

Unless otherwise noted, all component or composition levels are inreference to the active portion of that component or composition, andare exclusive of impurities, for example, residual solvents orby-products, which may be present in commercially available sources ofsuch components or compositions.

All percentages and ratios are calculated by weight unless otherwiseindicated. All percentages and ratios are calculated based on the totalcomposition unless otherwise indicated.

It should be understood that every maximum numerical limitation giventhroughout this specification includes every lower numerical limitation,as if such lower numerical limitations were expressly written herein.Every minimum numerical limitation given throughout this specificationwill include every higher numerical limitation, as if such highernumerical limitations were expressly written herein. Every numericalrange given throughout this specification will include every narrowernumerical range that falls within such broader numerical range, as ifsuch narrower numerical ranges were all expressly written herein.

Inks and 3-D Articles

For purposes of this specification, headings are not consideredparagraphs and thus this paragraph is Paragraph twenty-three of thepresent specification. The individual number of each paragraph above andbelow this Paragraph can be determined by reference to this paragraph'snumber. In this paragraph twenty-three, Applicants disclose an article,said article being three dimensional and having at least two differentscales of porosity, said article comprising a polymer, said polymerbeing a solid at 25° C. and having a degradation temperature of at least200° C., preferably a degradation temperature from about 200° C. toabout 520° C., preferably a degradation temperature from about 250° C.to about 520° C., more preferably a degradation temperature from about300° C. to about 520° C., most preferably a degradation temperature fromabout 350° C. to about 520° C., each of said two difference scales ofporosity scales being independently selected from macro-porosity,meso-porosity, and micro-porosity. The micro-porosity, or micro-scaleporosity, should be defined herein as void with a cross-sectional areaof 0.05 μm² to 1 μm². The meso-porosity, should be defined herein asvoid with a cross-sectional area greater than 1 μm² to 25 μm². Themacro-porosity is defined herein as void with a cross-sectional areagreater than 25 μm².

Applicants disclose an article according to Paragraph 0023 wherein saidpolymer comprises a material selected from the group consisting ofimide, polysiloxane, epoxide, sulfone, fluoropolymer and mixturesthereof, preferably said imide is a polyimide, said polysiloxane ispolydimethylsiloxane, said epoxide is a polyepoxide, said sulfone is apolysulfone and said fluoropolymer comprises tetrafluoroethylene, morepreferably said fluoropolymer is a polytetrafluoroethylene.

Applicants disclose an article according to Paragraphs 0023 through0024, said article being selected from the group consisting of cylinder,pipe, prism, ring, drum, sphere, ellipsoid, cone, pyramid, polyhedron,and cellular structure.

Applicants disclose an article according to Paragraphs 0023 said articlebeing selected from the group consisting of a cylinder, a pipe, a prism,a ring, a drum, a sphere, an ellipsoid, a cone, a pyramid, a polyhedron,a cellular structure and combinations thereof wherein said:

-   -   a) cylinder is a structure that has the same cross-section from        one end throughout the other end, while both ends should be        identical, flat and parallel to each other, and having a contour        of circle or oval.    -   b) pipe is a structure that has the same cross-section from one        end throughout the other end, while both ends should be        identical, flat and parallel to each other, and having a contour        of annulus.    -   c) prism is a structure that has the same cross-section from one        end throughout the other end, while both ends should be        identical, flat and parallel to each other, and having a contour        of any polygons.    -   d) ring is a structure that, tracing from an outline of circle        or any polygons, is having a cross-sectional area at any portion        of the outline.    -   e) drum is an internally hollow structure has the same        cross-section on one end and on the other end, while both ends        should be identical, flat and parallel to each other, and having        a contour of circle or oval.    -   f) sphere is a structure which surface is defined by a set of        points that are all at the same distance three-dimensionally        from a given point.    -   g) ellipsoid is a structure that consisting a surface that can        be obtained from a sphere described above, by deforming it by        means of directional scaling or by affine transformation.    -   h) cone is a structure with a three-dimensional geometric shape        that tapers from a flat base, with any shapes or contour, to an        apex point.    -   i) pyramid is a structure that, with outer surfaces in        triangular shape, with the number of the triangular outer        surfaces depending on the number of lines that constituted a        flat polygonal base, connect and converge to the point at a        distance above the flat base.    -   j) polyhedron is a structure that consisted of flat polygonal        faces connected at all straight edges that three-dimensionally        enclosing a space.    -   k) cellular structure is a structure that is built with a number        of repeated base unit, said a cell or lattice, with same contour        or geometrical shape in any scaling.

Applicants disclose an article according to Paragraphs 0023 through0026, said article a three-dimensional porous carbon structure,preferably said article is carbonized by heat treatment.

Applicants disclose an ink comprising, based on total ink weight:

-   -   a) from about 25% to about 50%, preferably, from about 30% to        about 45%; more preferably from about 35% to about 45%; most        preferably from about 38% to about 45% of a polymer, said        polymer being a solid at 25° C. and having a degradation        temperature of at least 200° C., preferably a degradation        temperature from about 200° C. to about 520° C., preferably a        degradation temperature from about 250° C. to about 520° C.,        more preferably a degradation temperature from about 300° C. to        about 520° C., most preferably a degradation temperature from        about 350° C. to about 520° C., preferably said polymer        comprises a material selected from the group consisting of        imide, polysiloxane, epoxide, sulfone, fluoropolymer and        mixtures thereof, preferably said imide is a polyimide, said        polysiloxane is polydimethylsiloxane, said epoxide is a        polyepoxide, said sulfone is a polysulfone and said        fluoropolymer comprises tetrafluoroethylene, more preferably        said fluoropolymer is a polytetrafluoroethylene.    -   b) from about 50% to about 75%, preferably, from about 50% to        about 70%; more preferably from about 50% to about 65%; most        preferably from about 50% to about 60% of a solvent, said        solvent having a solubility of at least of 0.1 g polymer/mL of        said solvent, preferably said solvent being selected from the        group consisting of oxygenated solvents, hydrocarbon solvents,        or halogenated solvents and mixtures thereof;    -   c) from about 0.3% to about 12%, preferably, from about 0.3% to        about 10%; more preferably from about 0.5% to about 10%; most        preferably from about 0.5% to about 8% of a non-solvent, said        non-solvent having a solubility of no more than 0.001 g        polymer/mL of said non-solvent, which should be defined as the        maximum mass amount of polymer in gram that can be dissolved by        one milliliter (mL) of solvent herein, should be no more than        0.001 g/mL, preferably said non-solvent being selected from the        group consisting of oxygenated solvents and hydrocarbon solvents        and mixtures thereof.

Applicants disclose an ink according to Paragraph 0028, wherein saidnon-solvent comprises water.

Applicants disclose an ink according to Paragraph 0028, wherein thesolvent and/or non-solvent are miscible and are anhygroscopic;preferably the solvent and non-solvent are anhygroscopic. When thesolvent and/or non-solvent are anhygroscopic the ink can be extrudedthrough a nozzle onto a substrate, with a custom capability to track inkdensity with respect to change in ink rheological behavior and torecalibrate speed or dimension during printing, to form single-layer ormultiple-layer structures, under a relative humidity level lower than10%.

Applicants disclose an ink according to Paragraphs 0028 through 0030comprising a particle having a size range of from about 5 nm to about 3μm; preferably from about 50 nm to about 1 μm; more preferably fromabout 50 nm to about 250 nm; most preferably from about 50 nm to about200 nm; preferably said particles comprise a material selected from thegroup consisting of fumed silica, glass bubbles, polyhedral oligomericsilsesquioxane and mixtures thereof. Such particles enhance the overallporosity, reduce the density and relative permittivity of Applicants'three dimensional articles.

Process of Making an Ink and Making an Article

Applicants disclose a process of making the ink of Paragraphs 0028through 0031, said process comprising combining:

-   -   a) a polymeric material;    -   b) a solvent, said solvent having a boiling temperature Ta    -   c) a non-solvent said non-solvent having a boiling temperature        Tb, said Tb being at least 40° C. higher than Ta, preferably        about 50° C. higher than Ta, more preferably about 60° C. higher        than Ta, most preferably more than 70° C. higher than Ta; said        solvent and non-solvent being miscible; and    -   d) optionally particles having a size range of from about 5 nm        to about 3 μm; preferably from about 50 nm to about 1 μm; more        preferably from about 50 nm to about 250 nm; most preferably        from about 50 nm to about 200 nm; preferably said particles        comprise a material selected from the group consisting of fumed        silica, glass bubbles, polyhedral oligomeric silsesquioxane and        mixtures thereof.

Applicants disclose a process of making an article, said processcomprising extruding the ink according to Paragraphs 0028 through 0031,said ink comprising a solvent having a boiling temperature Ta and anon-solvent having a boiling point Tb that is higher than said Ta, saidTb being at least 40° C. higher than Ta, preferably about 50° C. higherthan Ta, more preferably about 60° C. higher than Ta, most preferablymore than 70° C. higher than Ta, through a nozzle onto a substrate at arelative humidity level of at least 10%, preferably at a relativehumidity level of from about 12% to 25%, more preferably at a relativehumidity level of from about 15% to 22%, and at a temperature at least15° C. lower than said Ta, preferably 40° C. lower than said Ta, morepreferably more than 70° C. lower than said Ta.

Applicants disclose a process of making an article according toParagraph 0033, said process comprising:

-   -   a) placing said article in a bath, said bath comprising one or        more non-solvents, preferably said non-solvents are selected        from the group consisting of methanol, water, isopropyl alcohol        and mixtures thereof; and/or maintaining the temperature and        relative humidity conditions of Paragraph 0033 until the ink        undergoes phase inversion, preferably said temperature and        relative humidity conditions are maintained for about 12 hours        to about 168 hours, more preferably for about 24 hours to about        72 hours, most preferably for about 36 hours to about 48 hours;        preferably said article is placed in said bath before said        temperature maintenance;    -   b) optionally, heating and/or reducing the environmental        pressure of said article to remove residual solvent, preferably        at least 90% of said residual solvent is removed from said        article, preferably said article is simultaneously heated and        the environmental pressure of said article is reduced,        preferably said heating is conducted such that the temperature        is raised at a rate of 5° C./minute to reach a temperature that        is at least 15° C. below the solvent's Ta. Step a) is conducted        to promote additional porosity in said article while Step b) is        conducted to increase said article's mechanical rigidity. The        article's environmental pressure can be reduced by placing said        article under a vacuum. The rate and degree of vacuum should be        controlled to avoid deforming said article.

Applicants disclose a process of making an article according toParagraph 0034, said process comprising removing said non-solvent byheating and/or reducing the environmental pressure of said article, saidheating comprising heating said article to a temperature at least 20° C.lower than Tb, preferably 35° C. lower than Tb, more preferably about50° C. lower than Tb. The article's environmental pressure can bereduced by placing said article under a vacuum. The rate and degree ofvacuum should be controlled to avoid deforming said article.

Applicants disclose a process of making an article according toParagraph 0034, said process comprising removing said non-solvent byplacing said article in an extraction bath, said extraction bathcomprising a material that comprises one or more liquids that saidarticle is not soluble in but which the non-solvent is soluble in;preferably said material should be heated to a temperature that is plusor minus 10° C. of the lowest boiling point of said one or more liquids.

Test Methods

Ink rheology measurement: Ink rheology is reported as ink viscosity inPa·s and ink yield stress in Pa. Rheological measurement (e.g.,viscosity, yield stresses) of the 3D printing inks should be performedon a Discovery Hybrid Rheometer (TA Instruments) with test temperaturecontrolled at 25° C. by a Peltier plate. All measurements should be doneusing a parallel-plate geometry with a diameter of 25 mm and a gap sizeof 1 mm between the top and bottom plate. When loading the ink samplesfor rheological measurement, a thin layer of silicone oil must beapplied to cover the exposed surface of ink samples between the platesto prevent moisture adsorption and solvent evaporation duringmeasurements. The silicone oil is a liquid polymerized siloxane withmolecular formula [—Si(CH₃)₂O—]_(n) and a viscosity of 100 mPa·s,purchased from Sigma-Aldrich (now part of MilliporeSigma) with theproduct identification number of 85409. Steady shear (in a range of 0.01s⁻¹ to 100 s⁻¹) tests should be performed under a strain of 0.5% tomeasure ink viscosities, and oscillatory stress (1 Pa to 50,000 Pa)tests should be performed under a frequency of 1 Hz to measure ink yieldstresses. Zero-shear viscosity value of ink samples is determined usingthe ink viscosity value at 0.01 s⁻¹. Yield stress of ink samples shouldbe determined from a plot of measured storage moduli (G′) of inks as afunction of oscillation stress. A representative plot for yield stressdetermination should have measured ink storage modulus values plotted inthe y-axis and have the corresponding oscillatory stress plotted in thex-axis, with both axes rendered in logarithmic scale as in FIG. 1wherein: initial linear storage modulus (G′) 1; linear slope after thenon-linear deflection of storage modulus values 2 and the intersectionof extrapolation (I) and (II) 3 is shown. The oscillatory stress value,indicated by the x-axis of the plot, should be determined as the yieldstress of sample ink. Such plot should be referred as the yield stressdetermination plot herein. The yield stress should be determined as theoscillatory stresses representing the onset point of non-linear initialdrop of storage modulus (G′) of ink samples from the yield stressdetermination plot. To determine the onset point of non-linear initialdrop of storage modulus in the yield stress determination plot, anextrapolation (I) obtained from the initial 50% of the linear G′ valuesbefore the non-linear deflection should be taken and anotherextrapolation (II) based on the last 50% of the linear portion of the G′slope after non-linear deflection should also be taken. The onset pointshould then be determined by the intersection of extrapolation I and II,by which the corresponding oscillatory stress value of that point shouldbe defined as the yield stress value of the corresponding ink.

Density measurement: Density is reported as g/cm³. Density values ofprinted structures were determined following ASTM D-792 method at atemperature of 19° C. and using hexane as the immersion liquid. Porosityvalues were calculated from the measured densities, where

${{porosity}{value}(\%)} = {\left( {1 - \frac{{measured}{density}}{{bulk}{material}{density}}} \right) \times 100\%}$

The bulk material density in this case should be the density of thestructural starting material of the printed structures, as reported bythe manufacturer.

Tensile properties measurement: Tensile properties are reported asspecific tensile strength MPa/density and as specific modulusGPa/density. Tensile strength and modulus of the printed materialsshould be done on filamentary samples at a temperature of 25° C. basedon the slight modification of methods described by ASTM D3822 asdetailed below. Printed filamentary samples should be characterized byRSA III solid analyzer (TA Instruments) with a testing gauge length of10 mm and a strain rate of 1%/s used for all samples and trials. Thefilamentary samples to be measured should be mounted onto a paperloading frame FIG. 2 . with a length 1, width 2, and thickness 3 being25.4±2 mm, 10±2 mm, and 0.3±0.1 mm, respectively. Each paper loadingframe should have a circular hole 4 with a diameter of 6.4±0.1 mm,locating in the center of paper loading frame and cut-off portion 5. Thecenter should be defined as the intersection of the midpoints of lengthand width of the paper loading frame. During sample preparation fortensile property measurement, the subject filamentary sample should havea length of 30 mm and should be adhered onto a paper loading frame usinga section of 3M 33+ Electrical Tape (with a length of 8±2 mm and a widthof 5±1 mm) applied at each end of the filamentary sample to affixfilamentary sample to the paper loading frame. During the sample loadingstep, the sample along with the attached loading frame should be loadedby the fiber/film tensile testing clamps of by RSA III solid analyzer. Acustomized shim (FIG. 3 ) having 1 a shim length of 21.70±0.5 mm; 2 ashim width of 7.85±0.5 mm; a shim thickness of 0.8±0.5 mm; a pair ofcircular holes 4 for screw fitting each having a diameter of 3.45±0.25mm made of RGD8730-DM by Stratasys and is fabricated by a Connex3 Object260 printer using RGD8730-DM. Such shim should be placed between eachcontact surface between the sample-attached paper loading frame and theclamps of RSA III solid analyzer. The sample-attached paper loadingframe should be then positioned and affixed by the RSA testing clamps atdesignated gauge length, using a torque wrench at a torque of 12 cN·m.Before tensile property measurement, the paper loading frame should becut across the circular hole (FIG. 2 ) to avoid biased measurement fromthe paper loading frame. Each tensile test sample, should break in theregion at the midpoint or ±12.5% of the total sample length from themidpoint, if tensile properties measurement are performed properly. Atsuch point, the tensile strength in MPa and the modulus in GPa is thetensile strength in MPa and the modulus in GPa for purposes of thepresent application. Such properties and the measured density of thesample is then used to calculate specific tensile strength MPa/densityand specific modulus GPa/density.

Dielectric properties measurement: Dielectric properties are reposted asrelative permittivity and dissipation factor of the printed materialsshould be measured at a temperature of 25° C. following the parallelplate method or the three terminal method in ASTM D150. The measurementsinvolved sandwiching printed two-layer log-pile structures (with athickness of ˜0.8 mm) using an E4991B impedance analyzer and Keysight16453A Dielectric Material Test Fixture (Keysight Technologies) at afrequency range of 100 MHz to 1 GHz.

Thermal properties measurement: Thermal properties are reported as glasstransition temperature (Tg) and thermal degradation temperature (Td) indegrees Celsius (° C.). The Tg of the printed materials should bemeasured following methods described in ASTM D3418-15 with slightmodifications as provided below. Differential scanning calorimetry (DSC,Discovery 2500 by TA Instruments) was performed on the printed materialsto evaluate material Tg. 1.5 mg of printed material, should be choppedinto sections having a the long axis a length of 1 mm to 2 mm to form athin mat loaded in aluminum testing specimens for test samplepreparation. A fast heating scan from 0° C. to 400° C. at a rate of 30°C./min should be applied to the samples in nitrogen with subsequentquenching from 400° C. to −20° C. at the same cooling rate. The Tgshould be determined from the subsequent heating scan, said therepresentative scan, in nitrogen from 0° C. to 400° C. at a rate of 10°C./min. Determination of Tg of the curve from the representative scanwas obtained through the software TA Instruments Trios v4.3.1.39215. ForTg analysis, the representative scan should be loaded by the Triossoftware to render a plot with temperature ranging between 25° C. to400° C. plotted in x-axis and the corresponding normalized sample heatflow, with a unit of W/g, plotted in y-axis as in FIG. 4 showing startof first linear portion used for Tg determination 1; end of secondlinear portion used for Tg determination 2 and Tg value determined bythe software 3, read as Midpoint in the software-generated plot.

The rendered curve should have exothermic heat flow directed in thepositively increasing y-axis direction and the endothermic heat flowdirected in the negatively increasing y-axis direction, and the renderedcurve should span through at least 60% of the y-axis scale. Along therendered curve, in the direction of increasing temperature from 25° C.,a deflection of curve slope towards endothermic heat flow directionshould be observed, followed by another deflection of curve slope athigher temperature. Through the Trios software, select a portion of thecurve that covers from the linear portion of the curve at about 25° C.to 56° C. before the initiation of first slope deflection and until thelinear portion at about 25° C. to 56° C. after the second slopedeflection. The Tg of the curve should be obtained by selecting “Glasstransition” from the “Analyze” option of the selected curve. Thermalstability of the printed materials should be characterized followingmethods described in ASTM E2250-17, with the thermal gravimetricanalysis (TGA, Q500 by TA Instruments) performed on the printedfilaments to determined materials degradation over heat treatment from30° C. to 900° C. at a heating rate of 10° C./min under gas nitrogenhaving the a purity level 99.99%. The Td herein should be defined as thecorresponding temperature at the 5 weight percent loss during thedescribed thermal gravimetric analysis.

Cryofracturing of printed materials: To prepare for cryofracturing, 2 mgof printed material should be submerged in isopropyl alcohol(CH₃CHOHCH₃, with a purity level of 99.7% or higher) and capped in a 20mL glass vial (VWR product catalog number: 66009-562) at 25° C. for over12 hours before further use. During cryofacturing, the printed materialsshould be removed from the isopropyl alcohol and immediately submergedin a liquid nitrogen bath that should be kept in a dewar. Duration ofprinted material immersion in liquid nitrogen should be for 15 minutesto ensure proper cryogenic state of printed materials. While submergedin the liquid nitrogen bath, should be cut by a single-edge razor bladewith a blade thickness equal to or less than 0.009 inch. With propercryofracturing, sample cross sections, when being examined by a scanningelectron microscope, should display any crushing or distortion of thecross-sectional pores nor should they display deformation of thecross-sectional contour and integrity.

Void or pore size measurement: Measurement of void or pore sizes in theprinted materials should be done on the cross sections with necessarypost-printing treatments described in the Test Methods Section of thisspecification. Proper cross sections of printed materials should beconfirmed by morphology analysis before used for pore size measurement.The proper cross sections described herein should be obtained from (1)the fractured surfaces from samples undergoing tensile test described inthe tensile properties measurement or from (2) the cryofracturing ofprinted materials methods. From the proper cross sections, images of thesample cross section morphology should be taken in the orthogonal viewdirection to the targeted sample area, by a scanning electron microscope(ZEISS GeminiSEM 500) operated at an accelerating voltage of 2 kV with aworking distance less than 4.5 mm and a magnification of 1000×. Thecollected morphology images should be imported to an image processingprogram ImageJ (v1.8.0) developed by the National Institute of Health.The procedure of pore size measurement should include: (1) importcollected sample morphology images into ImageJ, (2) set the global scaleof unit length to pixel in the software, (3) select and duplicate targetarea for pore size measurement, (4) adjust threshold of the duplicatedimage until pore contours are clearly shown and make sure pores arecompletely filled by threshold selection, (5) apply the selectedthreshold and use built-in “Analyze Particles” function to measureselected pores by setting the to capture pores openings to sizes between0.05 μm² to 25 μm² and circularity between 0.05 to 1.00. This willreturn area measurement of pores captured by the program. (6) Import thepore area measurements to a spreadsheet in Microsoft Excel program andconvert the measured area values to corresponding diameters of circularpores, using the following equation. The calculated diameters werereported as pore size with a unit in μm.

$\begin{matrix}{{{pore}{size}\left( {\mu m} \right)} = {2 \times \sqrt{\frac{{measured}{individual}{porous}{area}\left( {\mu m}^{2} \right)}{\pi}}}} \\{= {{corresponding}{diameter}{of}a{circular}{pore}({\mu m})}}\end{matrix}$

EXAMPLES

The following examples illustrate particular properties and advantagesof some of the embodiments of the present invention. Furthermore, theseare examples of reduction to practice of the present invention andconfirmation that the principles described in the present invention aretherefore valid but should not be construed as in any way limiting thescope of the invention.

Example 1—Development and formulation of 3D printable phase-inversioninks containing polyimide and miscible good and poor solvent. To a 20 mLglass vial (VWR product catalog number: 66009-562) was added 11 gram ofN,N-Dimethylformamide and 1 gram of polyethylene glycol (with molecularweight ˜400 g/mol). The mixture was then capped and mixed via a vortexmixer for 15 minutes. To a separate 300-mL container was added 9 gram ofpolyimide solid Matrimid® 5218, then was added the previous mixture ofN,N-Dimethylformamide and polyethylene glycol. The ternary mixturecapped, and was then mixed using a planetary centrifugal mixer at aspeed of 2,000 rpm for 2 minute per session, with a total of 6 sessions.After mixing from the planetary centrifugal mixer, the container wasthen transferred onto a roller mixer kept at a speed of 50 rpm untilcomplete dissolution of the solids. The product formed after completedissolution was then referred as the ink. Throughout the wholepreparation process in Example 1, all steps were done under an ambienttemperature of 25° C.

Example 2—Extrusion and 3D printing of phase-inversion inks. To preparefor printing and ink extrusion, the ink was loaded into a syringeequipped with a nozzle with a typical diameter size of 250 or 580 μm.The syringe assembly, loaded with printing ink, was then be placed intoa Nordson EFD HPx high-pressure dispenser attached to a three-axisgantry system. During printing, desired toolpath for the gantry systemwas loaded through a controlling program or computer to move the gantrysystem to designated spaces, and a proper pressure was applied to thesyringe through the high-pressure dispenser to extrude ink onto targetsubstrate. The appropriate level of pressure to extrude the inks dependson the ink rheological behavior and nozzle size. If a tapered nozzlewith an inner diameter of 250 μm was used, an appropriate pressure levelto extrude would be ˜420 kPa for the ink described in Example 1. If atapered nozzle with an inner diameter of 580 μm was used, an appropriatepressure level to extrude the ink described in Example 1 would be ˜300kPa. A relative humidity level of 18% was found appropriate for 3Dprinting condition of the ink in Example 1 to undergo phase inversionwhile being printed into desired 3D structures. To prevent ink phaseinversion and avoid generation of intrinsic porosity of the printedstructures, a suppressed relative humidity level of 5% (with <5%tolerance) can be used during 3D printing process. Throughout the wholepreparation process in Example 2, all steps were done under an ambienttemperature of 25° C.

Example 3— Post-print phase inversion process. Printed structures fromExample 2 could be kept in ambient condition or placed in a bath topromote post-print phase inversion of the inks. For bath phase-inversionprocess, printed structures were placed in a 150-mL bath mixed withwater and methanol in a respective 92 to 8 percent ratio by weight. Thewater/methanol bath, acts as poor solvents for polyimide that exchangewith the residual ink solvent in the printed structure, can promotephase inversion process to increase resultant porosity of the printedstructures. During the post-print phase inversion process, in ambient orbath conditions, the printed structures were completely solidified.Throughout the whole preparation process in Example 3, all steps weredone under an ambient temperature of 25° C.

Example 4— Residual ink solvents extraction process. A further inksolvent extraction process was done by placing printed structures in a300-mL bath mixed with water and methanol in a respective 44 to 55percent ratio by weight, maintained at 60° C. for over 12 hours. A totalof 6 baths were applied to the printed structures to completely removethe ink solvents (N,N-Dimethylformamide and polyethylene glycol)described in Example 1. Alternatively, solvent extraction process canalso be done by treating printed structures in an oven with atemperature maintained above boiling points of ink comprising solventsunder vacuum.

Example 5—Development and formulation of alternative 3D printablephase-inversion inks containing polyimide and miscible good and poorsolvent. The procedure of Example 1 was used except the amount ofpolyethylene glycol (with molecular weight ˜400 g/mol) was varied to be0.1 or 0.5 gram to create gradient of the resulting porosity of theprinted structures.

Example 6—Development and formulation of alternative 3D printablephase-inversion inks containing polyimide and miscible good and poorsolvent. The procedure of Example 1 was used except the amount ofMatrimid® 5218 was changed to 7.5 gram.

Example 7—Development and formulation of alternative 3D printablephase-inversion inks containing polyimide and miscible good and poorsolvent. The procedure of Example 1 was used exceptN,N-Dimethylformamide and polyethylene glycol (with molecular weight˜400 g/mol) was replaced by N-Methyl-2-Pyrrolidone and glycerol,respectively.

Example 8—Development and formulation of alternative 3D printablephase-inversion inks containing polyimide and miscible good and poorsolvent. The procedure of Example 1 was used except polyethylene glycolwith a molecular weight of ˜400 g/mol is replaced by polyethylene glycolwith a molecular weight of ˜200 g/mol or ˜600 g/mol.

Example 9—Development and formulation of particles-loaded 3D printablephase-inversion inks containing polyimide and miscible good and poorsolvent. To a 20 mL glass vial (VWR product catalog number: 66009-562)was added 11 gram of N,N-Dimethylformamide and 0.7 gram of 3M™ GlassBubbles D32/4500. The mixture in 20-mL glass vial was sonicated whilemaintained in rotation at a speed of 30 rpm for two hours beforesubsequent addition of 1 gram of polyethylene glycol (with molecularweight ˜400 g/mol). The mixture capped and was then further mixed usinga planetary centrifugal mixer and a customized holder (FIG. 5A) havingplacement socket 1 for the 20-mL glass vial (VWR product catalog number:66009-562) and a layer of polydimethylsiloxane, with a thickness of 1mm, coated on the bottom surface of the socket; a placement socket 2 forthe 4-mL glass vial (Thermo Fisher Scientific product catalog number:B7999-2) and a layer of polydimethylsiloxane, with a thickness of 1 mm,coated on the bottom surface of the socket; (FIG. 5A) having cleat wedgedesign 3 to provide fixture during mixing; and holder material is madeof acrylonitrile butadiene styrene. The planetary centrifugal mixer anda customized holder (FIGS. 5A and 5B) is operated at a speed of 2,000rpm for 2 minute per session, with a total of 2 sessions. To a separate300-mL container was added 9 gram of polyimide solid Matrimid® 5218,then was added the aforementioned mixture of solvents and glass bubbles.The container capped, and was mixed using a planetary centrifugal mixerat a speed of 2,000 rpm for 2 minute per session, with a total of 6sessions. After mixing from the planetary centrifugal mixer, thecontainer was then transferred onto a roller mixer kept at a speed of 50rpm until complete dissolution of the solids. The product formed aftercomplete dissolution was then referred as the ink. Throughout the wholepreparation process in Example 9, all steps were done under an ambienttemperature of 25° C.

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While the present invention has been illustrated by a description of oneor more embodiments thereof and while these embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus andmethod, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope of the general inventive concept.

What is claimed is:
 1. A 3D printed article, said article being at leasta cylinder, a pipe, a prism, a ring, a drum, a sphere, an ellipsoid, acone, a pyramid, a polyhedron, a cellular structure and combinationsthereof and having at three different scales of porosity, said articleconsisting essentially of a polymer selected from the group consistingof imide, polysiloxane, epoxide, sulfone, fluoropolymer and mixturesthereof, porous carbon and a glass, said polymer being a solid at 25° C.and having a degradation temperature of at least 200° C. said threedifference scales of porosity scales being a macro-porosity, ameso-porosity, and a micro-porosity.
 2. The article of claim 1 whereinsaid polymer has a degradation temperature from about 350° C. to about520° C.
 3. The article of claim 1 wherein said imide is a polyimide,said polysiloxane is polydimethylsiloxane, said epoxide is apolyepoxide, said sulfone is a polysulfone and said fluoropolymercomprises tetrafluoroethylene.
 4. The article of claim 3 wherein saidfluoropolymer is a polytetrafluoroethylene.